Digging in one last time for the LHC

A landmark event occurred during the second week of March, when the final cubic metres of earth were cleared away, completing the excavation phase for the entire LHC project . The event took place at Point 5, where the CMS detector will be installed, as civil engineering teams finished digging the cavern that connects the LHC tunnel with the bypass tunnel around the experimental cavern. Two new access shafts, two large caverns, two ancillary caverns, as well as the connecting tunnels have been excavated by the civil engineering teams.

"The engineers heaved a huge sigh of relief when the work was done, because the excavations were quite risky. Anything can happen, and the risk of delays was far from zero," explains Jean Luc Baldy Head of ST Division's civil engineering group. This was especially true around Point 5, where unusual geology created some problems. The moraine-molasse interface lies 50 metres beneath the surface, or just about 18 metres above the roof of the caverns. Because the moraine consists of loose, unstable rock, the crews needed to find a means of preventing any risk of structures collapsing. Moreover, two areas of groundwater located one above the other within the same zone created an additional challenge. A ground-freezing technique was used to allow excavation under stable rock while also preventing an inflow of groundwater into the excavation. Today, the concreting work is under way throughout the excavated area and the CMS cavern should be fully complete by July 2004.